This invention relates to a method of manufacturing a gear case having two support cylinders inclined relative to each other.
A brush cutter includes a drive shaft driven by an engine and a rotary shaft inclined relative to the drive shaft. The rotary shaft is coupled to a joint shaft through bevel gears in a gear case connected to an elongated cylinder in which is mounted the drive shaft. The joint shaft is coupled to the driven shaft. Thus, torque is transmitted from the engine to the rotary shaft through the drive shaft, joint shaft and bevel gears.
Since the drive shaft and the rotary shaft are inclined relative to each other, they are inserted in and supported by two support cylinders of the gear case, which are inclined at the same angle as the inclination angle between the drive shaft and the rotary shaft. The joint shaft is rotatably supported by a single bearing or a combination bearing mounted on the inner wall of one of the support cylinders. The rotary shaft is rotatably supported by two bearings mounted on the inner wall of the other support cylinder so as to be axially spaced from each other.
In this arrangement, if the two bearings for supporting the rotary shaft are not precisely aligned with each other when pressed into the support cylinder, it would be difficult to press the rotary shaft into the bearings. Also, if the inclination angle between the axis of the single bearing mounted in one of the support cylinders and the axis of the two bearings mounted in the other support cylinder is inaccurate, the bevel gears mounted to the joint shaft and the rotary shaft tend to mesh incompletely. This makes it difficult to smoothly transmit torque from the joint shaft to the rotary shaft. Also, the bevel gears would produce rattling sound.
Thus, it is required to mount the bearings with high accuracy. In order to mount the bearings with high accuracy, it is necessary to finish the inner surfaces of the support cylinders by turning with high accuracy. But machining the inner surfaces of cylindrical objects with high accuracy is troublesome and time-consuming.
An object of the invention is to provide a method of easily manufacturing a gear case which has little error in the inclination angle.